The measurement of total serum protein is a summation of the concentration of the hundreds of different plasma proteins in the circulation. In practice only albumin, the immunoglobulins and to a lesser extent fibrinogen, are present in high enough concentrations to individually affect the total protein concentration. Changes in total serum protein concentration measurements may be due to changes in either the amount of the proteins in the circulation, or the amount of water in the circulation. Intra-vascular water may change due to whole body effects such as dehydration, or to redistribution of water within the body, eg prolonged tourniquet or postural changes. Changes in water distribution affect the measurement of a range of analytes in addition to total protein, eg albumin, lipids, red cell count, and total calcium. These are analytes which are too large, or are attached to carriers which are too large to pass though the blood vessel wall when there is a movement of water.

Serum has a total protein 3 – 5 g/L less than plasma due to the consumption of fibrinogen. Moving from a lying to standing position can increase total protein by 10% due to water redistribution. Prolonged application of the tourniquet can markedly increase total protein by forcing water out of the vascular compartment prior to sample collection.

Increased serum protein

• Increased immunoglobulins: monoclonal, polyclonal

Decreased intra-vascular water

• Dehydration
• Prolonged use of a tourniquet
• Standing compared to lying

Hypoproteinaemia                  top of page

Decreased serum protein

• Hypoalbuminaemia: malabsorption, malnutrition, liver disease, acute phase response
• Protein-losing states: nephrotic syndrome, protein-losing enteropathy, burns, third space losses, post-surgery